Project Summary This proposal seeks competitive renewal of the grant GM052872, which has been supporting our basic research on SR protein-specific kinases in the past two decades. In light of our recent discoveries that SRPKs are largely responsible for transducing growth factor signaling to regulate alternative splicing in mammalian cells, and SRPK1 is able to act either as an oncogene or tumor suppressor by regulating the recruitment of a critical Akt-specific phosphatase PHLPP1, we are in a unique position to attack novel tumorigenic mechanisms associated with altered SRPK1 function. As SRPK1 is the major kinase for SR proteins in most tissues (SRPK2 is restricted to the nerve system), we propose to focus in specific aim 1 on investigating its role in the transition from initial cell senescence to transformation. The proposed studies will determine its regulatory function on a recently elucidated ternary complex consisting of SRSF1 (an SR protein), MDM2 (an E3 ligase for p53), and RPL5 (a 60S ribosomal protein) to test the hypothesis that SRPK1 regulates the formation of the ternary complex to control the release of MDM2 from the complex to induce p53 destabilization. Given the synergy of the splicing kinase with other oncogenic signals observed on cellular models, we propose to determine such synergy in vivo by developing animal models in specific aim 2. We also propose to explore the biological significance of SRPK1 mutations on Akt-induced phosphorylation sites identified by the TCGA project. In the third specific aim, we propose to pursue a new chemical strategy to block SRPK1 because of new evidence that SRPK1 may be a key cancer target and characterization of a new SRPK1 inhibitor has generated a larger set of exciting results to suggest a great potential in developing the inhibitor as an effective anti-cancer agent. The proposed experiments in this aim will use the chemical tool to probe the mechanism of cancer signaling on the cell and animal models developed in the first two aims.